This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Sonic hedgehog (Shh) is a secreted molecule that regulates the postnatal development of the cerebellum, by promoting the proliferation of granule cell precursors (GCPs). Shh binds the patched receptor and activates smoothened. This triggers a cascade of events that involves several cytoplasmic proteins (Fused, SUFU, PKA, Costal, GSK3) and culminates with the activation of the GLI trancription factors (GLI1, GLI2 and GLI3). Deregulation of the Shh pathway is linked to neoplastic transformation of several tissues, including cerebellum, pancreas, prostate and skin. Compounds that block Shh transduction pathway, such as cyclopamine, are suppressors of neoplastic growth in vitro and in vivo. Therefore, the complete knowledge of the mechanisms of activation and repression of Shh represents a key aspect to generate drugs able to suppress tumor growth.